Measuring device with a reduced share of stray light

ABSTRACT

A device for measurement by means of a light ray is equipped with a covering device for reducing stray light. The device comprises an array of lenses along an optical axis; a prism attached to one of the lenses with a slanted surface for coupling of the light ray incident from a light source placed lateral to the optical axis, onto the optical axis, so that the light ray can pass through the array of lenses along the optical axis; a receiver for receipt of a share of the light ray reflected by an object; and a covering device for at least one area of the prism that scatters a share of the light ray as stray light to the receiver.

CROSS-REFERENCES TO RELATED APPLICATIONS

The present application claims priority to German Patent Application No.10 2009 028 861.9, filed Aug. 25, 2009, entitled “MEASURING DEVICE WITHA REDUCED SHARE OF STRAY LIGHT,” the disclosure of which is herebyincorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

The present invention relates to a device for measuring by means oflight rays, for example a distance-measuring device, with a reducedshare of stray light.

Measuring devices that use a light ray, such as laser beams, to forexample measure the distance between the measuring device and an objectof interest, are well known. In such devices a light beam is sent in thevisible or invisible range, such as a laser beam, through a lens arrayand a share of the light beam reflected by the object passes through thelens array again and is received by a detector of the measuring device.From the received signal, the distance of the measuring device to theobject can be derived, for example through measurement of path time orphase measurement of the emitted light signal to the received lightsignal.

Such known devices for measurement employing a light beam usually usethe optical lens array do not merely send and receive the light signalfor distance measurement, for example, but also use the lens array as anoptical device for searching for and aligning the device to the objectof interest. For this purpose, an eyepiece can be made available to theuser, or a sensor for generating an image on a screen.

One distance-measuring device is known from US 2006/0114448. In thisdistance-measuring device, a prism is connected to a lens array, tocouple laterally emitted light into an optical axis. The mirror or prismis placed in the central area of the lens array on the optical axis.Measurement light reflected from an object is collimated by the lensarray and directed to a detector that preferably lies in the focus ofthe array. Since the detector, viewed optically, is behind the coupledprism, not all the light that is reflected from the object reaches thedetector array. The detector can receive only such light reflected fromthe object as usable light, which is incident through the optical lensarray and past the prism to the detector.

Due to placement of the prism in the optical path of the lens array andbecause the prism is designed to be small, to permit as much measurementlight as possible to be incident on the receiver, especially when themeasurement light is coupled into the optical path through the mirror orprism, crosstalk effects result, which impair the quality of themeasured result. Stray light or reflected light generated in themeasuring device by the light beam can be incident on the receiver asstray light, and impair the ratio of usable light to stray light.

In the process of overall technical development it is desirable to beable to measure greater distances to the object, and thus use lightsources with greater power output. With a higher power class, forexample with a stronger laser, stray light also becomes greater and theprecision of the measured result is determined by the ratio of usablelight to stray light. Therefore, in such devices with a greater powerclass, the dynamic range must be expanded. When distance is measured,the stray light is included, and thus, for example, when usable lightundergoes a fourfold amplification if a higher power class for exampleis used, stray light is increased by a factor of 4, which does notincrease the dynamic range, i.e., the distance from usable light tostray light.

SUMMARY OF THE INVENTION

Therefore, it is desirable to further improve the dynamic range for adevice to measure using a light beam. Especially it is desirable, in adevice for measuring by means of a light beam to reduce the share ofstray light incident on the receiver which is generated within thedevice.

This problem of the invention is solved by the features of theindependent patent claims. Advantageous embodiment forms are found inthe dependent patent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a device for measurement by means of a light beam as per anembodiment form of the invention.

FIGS. 2 a and 2 b show examples of a prism with a covering device toeliminate stray light as per embodiment forms of the invention. Theprism can be used, for example, in the device as per FIG. 1.

FIG. 3 shows a prism for a device for measuring by means of a light rayas per an embodiment form of the invention, with a covering device toeliminate stray light on a slanted surface of the prism.

FIG. 4 shows a prism for a device for measurement by means of a lightray as per an embodiment form of the invention, with a covering deviceto eliminate stray light that has a frame shape.

FIG. 5 shows a prism for a device for measurement by means of a lightray as per an embodiment form of the invention, with a covering deviceto eliminate stray light, which is placed on the slanted surface of theprism.

FIGS. 6 a, 6 b and 6 c show views of a covering device for a device formeasurement by means of a light ray as per one embodiment form of theinvention. The covering device can be mounted on a prism on a slantedsurface.

FIG. 7 shows an array of a device for measurement by means of a lightray as per a further embodiment form of the invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a schematic arrangement of a device for measurement bymeans of a light ray according to one embodiment form.

Generally, for example, the device can be used in measurement orsurveying devices with a telescope or camera as a distance measuringdevice. Light to measure, for example, the distance to an object iscoupled to the optical axis and measurement light reflected from theobject is detected and evaluated by the receiver. Very generally thedevice can however be used to measure by means of a light ray, in everyoptical device in which an optical telescope is used for measurementcoaxial to a light ray. A laser source or another light source can beused as the light source.

The device for measuring by means of a light ray as per the presentembodiment form comprises an array of lenses 100 along an optical axis110, a prism 120 placed on one of the lenses with a slanted surface 130for coupling the light ray incident from a light source 140 lateral tothe optical axis onto optical axis 110, so that the light ray passesthrough the array of lenses 110 along optical axis 110. A receiver 150for receipt of a share of the light ray reflected by an object is madeavailable. Further, according to the invention, a covering device 160 ismade available for at least one area of the prism that scatters a shareof the light ray as stray light. The stray light can be a reflected orscattered share of the light ray.

Since the measurement light reflected back is an order of magnitude lessthan the emitted measurement light, the received reflected measurementlight must be detected by sensitive devices. One problem with suchsensitive receiving devices is stray light that is incident on thereceiver along with usable light reflected by an object. The precisionof the measurement process is determined by the ratio of usable light tostray light, i.e. on the ratio of the received measurement lightreflected from the object to the stray light. Sources of stray light arelight sources that not only lie outside the device, but stray light isalso generated within the device for measuring by means of a light ray,and in fact especially by scattering or reflection of the light ray thatis emitted by light source 140. This light ray is reflected or scatteredon components of the device, and is directly or indirectly incident onreceiver 150, thus increasing the share of stray light.

The light ray is particularly scattered or reflected when the light rayis coupled to the optical axis through edges of prism 120 or at thepoint of connection of prism 120 with the lens array 100. For couplingof the light ray from light source 140 onto optical path 110, the prism120 is preferably placed in the center area of lens array 100, thus inthe path of the light ray reflected from the object. Therefore, straylight arising through the prism when the light ray is coupled onto theoptical path is especially disadvantageous, because it is generated inthe reception path and is incident on receiver 150.

Therefore it is especially desirable to reduce stray light when thelight ray is coupled into optical path 110 on prism 120. For example, alarge prism could be used, so that the light ray is incident only in thecentral area of the prism onto slanted surface 130, not onto the edges,and thus stray light is eliminated. However, a larger prism also coversa larger area of the reception path, which causes usable light comingfrom the receiver to be lessened. A further possibility would be to makeavailable an apertured partition on light source 140, to reduce straylight emitted from light source 140. However, apertured partitions causeoptical effects that impair the usability of the light ray, and inaddition reduce the intensity of the measurement light, which obviouslyis not desirable.

Therefore, according to the present embodiment example, covering device160 is made available, which covers those areas of prism 120 thatparticipate in generating stray light due to the incident light ray formeasurement. Covering in this regard may mean that the covering deviceis so placed that the light ray is not incident on scattering orreflecting areas of the prism, such as the edge area of the prism, orthat the covering device is so placed that a light ray scattered byareas of the prism is hindered from being incident on receiver 150. Thecovering device does not have to lie directly on the scattering orreflecting area of the prism, but rather it may suffice if the coveringdevice lies in the propagation path of the stray light in the directionof the receiver.

One schematic example for a covering device 160 is shown in FIG. 1, andhere it covers the upper area of slanted surface 130 in the area of theupper edge of the prism. The upper edge area on slanted surface 130 ofthe prism is especially disadvantageous when stray light is generated,since the edge can have a chamfer, i.e. the edge may be slanted orchamfered, and thus participate especially in the generation of straylight. However, the embodiment forms described here are not limited tothe shown form of covering device 160, the covering device as alsodescribed in additional embodiment forms can be placed at this oranother place on the prism in various forms.

In advantageous fashion the covering device 160 is configured so that itprevents stray light from being generated through the emitted light beamfrom light source 140, or [prevents] stray light generated throughreflection or scattering of the light ray from being incident onreceiver 150. However, at the same time it is so placed that as small ashare of usable light as possible, i.e., of measured light reflectedfrom the object, is covered, i.e. prevented from being incident onreceiver 150. Thus, as viewed in the direction of the optical axis, thecovering device has a small extension going out over the lateralsurfaces of prism 120, so that only a little usable light that passesthrough lens array 100, is shadowed by the covering device. However,along the optical axis the extension of the covering device can begreater, since areas of the covering device which lie parallel to theoptical axis, scarcely shadow any received light.

For example, the covering device may project out over a cross sectionlying at a right angle to the optical axis of the prism by a lengthwhich is chosen so that the ratio of usable light to stray light ismaximal. The usable light is a share of the measurement light incidenton the receiver, reflected by the object, and the stray light is a shareof the measured light incident on the receiver that is reflected orscattered by the prism.

The array shown in FIG. 1 is an example. The invention-specific devicefor measurement by means of a light ray is not limited thereto. Forexample, covering device 160 can have another form and be in anotherposition. If received light is directed to the receiver by mirrors orsimilar devices, receiver 150 can be placed at an angle to axis 110 inFIG. 1.

Additionally, a control and evaluation device, not shown in FIG. 1, canbe provided, to evaluate the received signal at receiver 150, and forexample, compute a distance to an object. Such evaluation andcomputation procedures are generally known from prior art, and requireno further explanation at this point.

In addition, the control device can be arranged to focus the device bymeans of the lens array on an object of interest. The lenses can forexample be shifted relative to each other for focusing, as is generallyknown.

Additionally, the device can be equipped with a target-search devicewhich makes it possible for a user, for example by means of an eyepiece,to align the device through the lens array on an object of interest andappropriately focus it. As an alternative, a camera can also be situatedto depicted a scenario detected by the device, and correspondingly tofocus on an object of interest. Additionally, a device can be situatedto automatically track an object, for example by image processingprocedures carried out in the control device and correspondingly markedor shaped objects of interest.

As an example, in FIG. 1, light source 140 is placed at right angles tothe optical axis of the device. For coupling of the light ray emitted bylight source 140, the prism therefore has a slanted surface 130 tiltedby 45°, as is evident in FIG. 1. However, alternatively, light source140 can be placed not at right angles to optical axis 110, and the prismmay have a tilted slant surface 130 that has a different tilt, to couplethe light ray emitted from the light source onto the optical axis.

The lens array 100, the prism 120, the light source 140 and the receiver150 are known from prior art and require no further explanation at thispoint.

One manufacturing process for the device for measurement by means of alight ray as per FIG. 1 comprises placement of lenses 100 along anoptical axis 110; placement of a prism 120 on one of the lenses, withthe prism having a slanted surface 130, for coupling of the light rayincident from a light source 140 placed lateral to the optical axis ontothe optical axis 110, so that the light ray can pass through the arrayof lenses 100 along optical axis 110; placement of a receiver 150 forreceipt of a share of the light ray reflected by an object; andplacement, on the prism, of a covering device 160 for at least one areaof the prism that scatters or reflects a share of the light ray as straylight to the receiver.

FIGS. 2A and 2B show an embodiment form of a prism for the array formeasurement by means of a light ray from FIG. 1.

Here, prism 120 has a slanted surface 130, to couple the measurementlight from light source 140, shown in FIG. 2A, into the optical path asshown for example in FIG. 1. In manufacturing a prism for a device formeasurement by means of a light ray as per the invention, as shown inFIG. 2A, usually the edge 131 of the slanted surface that forms an acuteangle with the surface of prism 120 is chamfered or slanted, to preventformation of fragments and roughness in the edge area during the cuttingand grinding process.

The light ray from the light source, for example light source 140 fromFIG. 1, is incident along direction 201 in FIG. 2A on slanted surface130, and, due to the 45° inclination of the slanted surface, the lightray is coupled along direction 202 onto the optical axis. A part of thelight ray that is incident along direction 201 from the light source toslanted surface 130, is, however, reflected or scattered from the cantededge 131, and uses a direct path to get inside the device, i.e., not viathe object, to receiver 150 from FIG. 1. To prevent the light ray fromthe light source from impinging on canted edge 131, a covering device160-1 is attached on canted edge 131, which prevents measurement lightemitted from light source 140, illustrated by arrow 203, from beingdirectly incident on edge 131. Generally with this embodiment form, atleast one edge of the prism is covered on the slanted surface of theprism so that the light ray emitted by the light source is not incidenton the at least one edge.

Preferably covering device 160-1 has an antireflection coating or is ofantireflecting material and provided with edge areas not rounded off, soit generates as little stray light itself as possible. As illustrated inFIG. 2A, covering device 160-1 is situated in the same plane or placedparallel to a plane in which the upper side 210 of prism 120 is located.However, also covering device 160-1 can be inclined relative to surface210 of prism 120, for example with the edge lying away from the prismdirected upwards.

Alternatively, the covering device can comprise a non-reflecting coatingon a section of the prism.

Covering device 160-1 can be glued onto prism 120 in the area of uppersurface 210, or be mounted or attached to the prism with lateral straps.

In advantageous fashion, prism 120 like the entire device formeasurement by means of a light ray, as shown for example in FIG. 1, canbe manufactured in a conventional manner. Only in a further processingstep is covering device 160 or 160-1 attached to prism 120, which makesit possible that prism 120 does not have to be ordered with additionaladaptations.

FIG. 2B shows an additional embodiment form of prism 120, for examplefrom FIG. 1, to prevent stray light from being generated throughincident measurement light from a light source, for example light source140 in FIG. 1. The light source is not shown in FIG. 2B, but it can besituated as shown in FIG. 2A. As per 2B, similar to covering device160-1 from FIG. 2A, a covering device 160-2 is now made available thathas an edge which is rounded lying in the direction of the lens array.Since the light ray of the light source, such as a laser source, has acircular or elliptical cross section, the form of covering device 160-2in FIG. 2B can prevent the light ray from being excessively screened bythe covering device, and not able to be fully coupled into the opticalpath. One possible area of incidence of the light ray such as laserlight from light source 140 is illustrated in FIG. 2B at referencesymbol 220.

Also, covering device 160-2 prevents the light ray from light source 140from being directly incident on edge 131. The other features of coveringdevice 160-2 may be similar to covering device 160-1.

FIG. 3 shows another embodiment form of the covering device to reduce oreliminate stray light, for example for the device for measurement bymeans of measurement light as per FIG. 1. FIG. 3 show a possibleembodiment form of the covering device, 160-3, which is attached in thearea of slanted surface 130 of prism 120. Covering device 160-3preferably projects beyond canted edge 131 of the prism to the extentthat stray light or reflected measurement light possibly formed at edge131 cannot impinge directly on the receiver. For example, edge 160-31 ofcovering device 160-3 may lie in the plane that is formed by upper side210 of prism 120, so that measurement light from the lens array passingby on prism 120 is not prevented from being incident on the receiver.

Generally with this embodiment form, at least one edge of the prism iscanted, and the covering device is attached on the slanted surface ofthe prism so that it covers stray light from the at least one cantededge of the prism on the slanted surface of the prism so that the straylight from the edge is not incident on the receiver.

Covering device 160-3 can for example be glued on slanted surface 130and partially cover it, as shown in FIG. 3. Alternatively, coveringdevice 160-3 can also cover the entire slanted surface 130. The otherproperties of covering device 160-3 correspond to those of the coveringdevices of FIGS. 2A and 2B.

FIG. 4 shows another embodiment form of a covering device to eliminatestray light for a prism as for example prism 120 from FIG. 1.

In the process of manufacturing the device, for example the device fromFIG. 1, prism 120 normally is glued onto lens array 100. Depending onthe manufacturing process, a small quantity of adhesive gets compressedout of the area where the prism adjoins the lens array, in the area ofsurface 220 of the prism, and forms an adhesive bead, even if the frontside of the prism is canted.

It was explained above that due to slanted surface 130 of the prism, themeasurement light is coupled into the optical path. With this, parts ofthe measurement light also are incident on the above-mentionedprojecting adhesive or the adhesive bead in the area of edge 134, andthere are reflected or scattered. The stray light from these areas ofthe prism and the lens array are reflected or scattered in the directionof the receiver, for example receiver 150 from FIG. 1, and impair theproperties of the device.

For screening of such a type, for example, of stray light, according tothe embodiment form in FIG. 4, a screening device 160-4 is provided,which encircles prism 120 in the shape of a frame. Since stray lightgenerated at the location of adhesion is directed outside the prism inthe area of the surface of the prism in the direction of the receiver,covering device 160-4 can prevent this stray light from being incidenton the receiver, for example receiver 150 from FIG. 1. Preferably,covering device 160-4, at right angles to optical axis 110 from FIG. 1has a recess, which covers stray light from the area where prism 120 andlens array 100 are connected, but usable light that is reflected fromthe object and passes through lens array 100 only to a small degree.

Generally speaking, with this embodiment form, the covering devicecovers stray light generated at the location where the prism isconnected with one of the lenses so that the stray light is not incidenton the receiver. The thickness of the covering device at the locationwhere it covers at least one of the sides of the prism is chosen so thatthe covering device covers stray light from one edge of the prism at thepoint of connection with one of the lenses. Additionally, the thicknessof the covering device at the location where it covers at least one ofthe sides of the prism can be chosen so that the covering device coversstray light from an adhesive bead at the point where the prism isconnected with one of the lenses.

In addition, covering device 160-4 can be placed to prevent propagationof stray light as effectively as possible in the immediate vicinity ofthe connection area of the prism with the lens array, or also at anotherplace in the path of the stray light to receiver 150.

Preferably covering device 160-4 is optimized so that the ratio ofusable light to stray light is the greatest. In other words, coveringdevice 160-4 is so arranged and dimensioned that the ratio of usablelight reflected from the object of interest that is incident on receiver150 to the stray light generated in the area of the device itself, whichis incident on receiver 150, is maximal.

In other words, in this embodiment form, the covering device can projectover a cross section placed at right angles to the optical axis of theprism by a projecting length, with the projecting length being chosen sothat the ratio of usable light to stray light is maximal. The usablelight is a share of the measurement light incident on the receiver,reflected from the object, and the stray light is a share of the lightray incident on the receiver that is reflected or scattered from theprism.

FIG. 6 shows an additional embodiment form of a covering device toprevent stray light that is generated at prism 120, for example of thedevice from FIG. 1, from being incident on receiver 150.

The covering device from FIG. 5, covering device 160-5, is attached inthe area of slanted surface 130 of the prism, and is provided for thisto prevent stray light generated in the area of canted edge 131 on theslanted surface from being incident on the receiver, as well as toprevent stray light generated at the point where prism 120 is connectedwith lens array 100 from being incident on receiver 150.

For this, covering device 160-5 is dimensioned so that it projects outon one side, but preferably on every side of slanted surface 130 overthe slanted surface, and in fact so that also in the area of canted edge131 it projects over an imaginary extension of the upper side of prism210.

Due to the arrangement, stray light formed on canted edge 131 isscreened off, and also stray light generated at the point where theprism is connected with the lens array, which runs in the vicinity ofthe surface of the prism in the direction of the receiver, is likewiseeffectively screened off.

As previously in the arrangement of FIG. 4, the projecting length ofcovering device 160-5 over the lateral surfaces of the prism or over theextension of lateral surface 210 of the prism is of such type that theratio of usable light incident on the receiver to stray light ismaximized.

FIGS. 6A, 6B and 6C show another embodiment form of covering device 160from FIG. 1. FIG. 6A shows a side view of covering device 160-6. FIG. 6Bshows a top view of the covering device and FIG. 6C shows a slanted viewof the covering device.

Covering device 160-6 from FIGS. 6A, 6B and 6C is open on one side andbox-shaped, and can be placed on slanted surface 130 of prism 120, andcover at least two of the lateral surfaces of the prism at leastpartially.

For this, the covering device has a back surface 610 which adjoinsslanted surface 130 of the prism, as well as a lateral surface 630 whichadjoins surface 210 of the prism, a lateral surface 640, which adjoinsthe side of the prism opposite surface 210, and lateral surfaces 620 and650, which likewise adjoin the lateral surfaces of prism 120.

Lateral surface 630, as shown in FIG. 6B, has a rounded recess, to be aslittle hindrance as possible to the circular or elliptical cross sectionof the light ray, as already described with reference to FIG. 2B.However, as shown in FIG. 2A, surface 630 of the rounded recessalternatively can have a straight edge. An example of such a straightedge is designated in FIG. 6B by 631. Preferably lateral surface 630 isdimensioned so that, as viewed in the direction of the light ray fromlight source 640, it covers only canted edge 131 or slightly more thancanted edge 131, and thus does not lie over lateral surface 210 of theprism or only slightly so, so as not to lie in the propagation path ofthe light beam. In contrast, sides 620, 640 and 650 can project furtherover the particular lateral surfaces of the prism, since they do not liein the area of light ray propagation.

Preferably, the lateral surfaces and back surface 610 of covering device160-6 are shaped so that the covering device can be placed onto theprism in the area of slanted surface 130, and has clamped contact withit, so that the covering device cannot get loose by itself from theprism, even when subjected to shaking. Alternative or additional tothis, the covering device also can be glued to prism 120.

FIG. 7 shows another embodiment form of the device for measurement bymeans of a light ray.

The device according to FIG. 7 shows a lens array 701 with lenses 701 aand 701 b, that define an optical axis 700. On lens axis 700, a focusinglens 704 and crosshairs 705 are placed.

As known from prior art, focusing lens 704 is movable, to focus incidentlight onto crosshairs 705. The image can be viewed through an eyepiece706. For the lens, and preferably in the interior area of lens 701 b, aprism 702 is made available, with a reflecting surface 703 on theoptical axis 700. Surface 703 of prism 702 can have a dichroic coating.Prism 703 serves to reflect light rays lambda λ1 and λ2 fromtransmitters 711 and 712, for example laser transmitters, orlaser-emitting diodes, to make available a transmission light path. Thelight is directed outward through lens array 701 in the direction of atarget lens.

The prism has a lateral surface tilted by 45°, and thus causes a 90°deflection of incident light of the incident light of light rays X1 andX2. The light rays reach the prism at right angles to the optical axis,and thus are coupled into the optical axis. This simplifies thearrangement, as already explained for FIG. 1, but is not necessary.Other arrangements than right-angle are possible for light rays λ1 andλ2.

The two light rays λ1 and λ2 emerge coaxially from lens array 701, asshown in the figure. For this, the transmitters are so arranged thatrays λ1 and λ2 are each reflected on a mirror 713 and 714, so that thelight rays reflected in such a way form the coaxial ray that is incidenton prism 702.

The light reflected from the object reaches lens array 701 as a ray thatconsists of the transmitting wavelengths, and which normally is expandedso that it covers the entire lens area. It is understood that the prism702 is small with regard to the entire area of lens array 702, and thuscovers only a relatively small part of the reflected light.

Viewed in the direction of the optical axis, prism 702 may have arectangular or square cross section. However, it is also possible thatthe prism does not have a cross section with radial symmetry, to reducethe covering of the share of light reflected from the target object.

Two dichroic plates 721 and 722 are placed in tipped fashion in thereflected light ray on optical axis 700 between prism 702 and crosshairs705. In this connection, tipped means that they are not placed at rightangles to the optical axis. Thus a part of the light ray with thewavelength lambda 1 is reflected at the first tipped plate 721 in thedirection of mirror 731, which in turn reflects the light ray in thedirection of detector 741. In the same manner, the other part of the raywith the wavelength lambda 2 passes through first plate 721 and isincident on second tipped plate 722, where it is reflected, in thedirection of second mirror 732, which in turn reflects the ray in thedirection of a detector 742. The two receivers or detectors 741 and 742are placed outside light path 709, which is formed by lens 701.

In the present embodiment example, an additional emitter 715 is placedat right angles to the optical axis, and this emitter can emit awavelength λ3. This light ray with wavelength λ3 can for example be usedto emit a visible ray to align the device to a target.

The reflected light detected from the object by receivers 741 and 742can be evaluated to derive for example a measured distance to theobject, as is known from prior art.

In its present embodiment form, prism 702 in FIG. 7 is configured as itwas described with reference to one or more of the foregoing figures. Asan example, in FIG. 7 the covering device 760 is shown.

A manufacturing process for a device for measurement by means of a lightray may comprise: placement of lenses along an optical axis; placementof a prism on one of the lenses, whereby the prism has a slantedsurface, for coupling of a light ray from a light source placed lateralto the optical axis into the optical axis, so that the light ray canpass through the array of lenses along the optical axis; placement of areceiver for receipt of a share of the light ray reflected from anobject; and placement, on the prism, of a covering device for at leastone area of the prism that scatters or reflects a share of the light rayas stray light to the receiver.

The covering device can be so attached that it covers at least an edgeof the prism on the slanted surface of the prism, so that the light rayemitted by the light source is not incident on the at least one edge.

Additionally with the manufacturing process, at least one edge of theprism can be canted and the covering device can be attached to theslanted surface of the prism and cover stray light from the at least onecanted edge of the prism on the slanted surface of the prism so thatstray light from the edge is not incident on the receiver.

Additionally, the covering device can be attached so that it coversstray light generated at the point where the prism is connected with oneof the lenses so that the stray light is not incident on the receiver.

At any point during manufacturing, the covering device can be placed onthe prism and at least partially cover at least two of the lateralsurfaces of the prism.

The covering device can be chosen to provide less coverage of thelateral surface of the prism, on which the light ray emitted from thelight source is incident, than coverage of other covered lateralsurfaces.

Additionally, the thickness of the covering device at the location whereit covers at least one of the sides of the prism, can be chosen so thatthe covering device covers stray light from an edge of the prism at thepoint of connection with one of the lenses.

The thickness of the covering device at the location where it covers atleast one of the sides of the prism can be chosen so that the coveringdevice covers stray light from an adhesive bead at the point ofconnection of the prism with one of the lenses.

Lastly, the covering device can also be dimensioned so that it projectsover a cross section lying at right angles to the optical axis of theprism by a projecting length. The excess can be so chosen that the ratioof usable light to stray light is maximal. The usable light is a shareof the measurement light reflected from the object and incident on thereceiver, and the stray light is an undesired share of the measurementlight incident on the receiver that is reflected or scattered from theprism, incident on the receiver.

With the manufacturing process for the embodiment forms described above,the covering device may be attached at a suitable time, or an existingmeasuring device can be retrofitted, by attaching the covering deviceafter manufacturing.

1. A device for measurement by means of a light ray, the deviceincluding: an array of lenses along an optical axis; a prism attached toone of the lenses with a slanted surface for coupling of the light rayof the light source placed lateral to the optical axis onto the opticalaxis, so that the light ray can pass through the array of lenses alongthe optical axis; a receiver for receipt of a share of the light rayreflected from an object; and a covering device for at least one area ofthe prism that guides a share of the light ray as stray light to thereceiver, whereby the covering device is attached on the prism.
 2. Thedevice of claim 1 whereby the covering device covers at least one edgeof the prism on the slanted surface of the prism so that the light rayemitted by the light source is not incident on the at least one edge. 3.The device of claim 1 whereby at least one edge is canted and thecovering device is attached to the slanted surface of the prism andcovers stray light from the at least one canted edge of the prism sothat the stray light is not incident on the receiver.
 4. The device ofclaim 1 whereby the covering device covers stray light generated at thepoint where the prism is connected with one of the lenses, so that thestray light is not incident on the receiver.
 5. The device of claim 1whereby the covering device is placed on the prism, and at least two ofthe lateral surfaces of the prism are at least partially covered.
 6. Thedevice of claim 5 whereby a covering of the lateral surface of the prismby the covering device on which the light ray emitted by the lightsource is incident, is less than a covering of the other covered lateralsurfaces.
 7. The device of claim 1 whereby the thickness of the coveringdevice at the location where it covers at least one of the sides of theprism, is chosen so that the covering device covers stray light from anedge of the prism at the point of connection with one of the lenses. 8.The device of claim 1 whereby the thickness of the covering device atthe location where it covers at least one of the sides of the prism ischosen so that the covering device covers stray light from an adhesivebead at the point where the prism is connected with one of the lenses.9. The device of claim 1 whereby the covering device has anon-reflective surface and unrounded edges.
 10. The device of claim 1whereby the covering device comprises a non-reflective coating of anarea of the prism.
 11. The device of claim 1 whereby the covering deviceprojects over a cross section lying at right angles to the optical axisof the prism by a projecting length, and whereby the projecting lengthis chosen so that the ratio of usable light to stray light is maximal,whereby the stray light is a share of measurement light incident on thereceiver reflected from the object, and the stray light is a share ofmeasurement light incident on the receiver which is reflected orscattered by the prism.
 12. A manufacturing process for a device formeasurement by means of a light ray, the manufacturing processincluding: placement of lenses along an optical axis; placement of aprism on one of the lenses, whereby the prism has a slanted surface forcoupling of the light ray incident from a light source placed lateral tothe optical axis onto the optical axis so that the light ray can passthrough the array of lenses along the optical axis; placement of areceiver for receipt of a share of the light ray reflected from anobject; and placement, on a prism, of a covering device for at least apart of the prism that scatters a share of the light ray as stray lightto the receiver, whereby the covering device is attached on the prism.13. The manufacturing process of claim 12 whereby the covering device isattached so that it covers at least one edge of the prism on the slantedsurface of the prism, so that the light ray emitted from the lightsource is not incident on the at least one edge.
 14. The manufacturingprocess of claim 12 whereby at least one edge of the prism is canted andthe covering device is placed on the slanted surface of the prism andcovers stray light from the at least one canted edge of the prism sothat the stray light is not incident on the receiver.
 15. Themanufacturing process of claim 12 whereby the covering device isattached so that it covers stray light generated at the point where theprism is attached with one of the lenses so that the stray light is notincident on the receiver.
 16. The manufacturing process of claim 12whereby the covering device is placed on the prism and at leastpartially covers two of the lateral surfaces of the prism.
 17. Themanufacturing process of claim 16 whereby one covering of the lateralsurface of the prism by the covering device on which the light rayemitted by the light source is incident, is selected to be smaller thana covering of the other covered lateral surfaces.
 18. The manufacturingprocess of claim 12 whereby the thickness of the covering device at thelocation where it covers at least one of the sides of the prism ischosen so that the covering device covers stray light from an edge ofthe prism at the point of connection with one of the lenses.
 19. Themanufacturing process of claim 12 whereby the thickness of the coveringdevice at the location where it covers at least one of the sides of theprism is so chosen that the covering device covers stray light from anadhesive bead at the point where the prism is connected with one of thelenses.
 20. The manufacturing process of claim 12 whereby the coveringdevice has a non-reflective surface and unrounded edges.
 21. Themanufacturing process of claim 12 whereby the covering device comprisesa non-reflective coating of an area of the prism.
 22. The manufacturingprocess of claim 12 whereby the covering device is placed so that itprojects over a cross section lying at right angles to the optical axisof the prism by a projection length, and whereby the projection lengthis chosen so that the ratio of usable light to stray light is maximal,whereby the usable light is the share of measurement light reflectedfrom the object, incident on the receiver, and the stray light is anundesired share of the measurement light reflected or scattered by theprism which is incident on the receiver.